1. Field of the Invention
The present invention relates to a process for producing L-threonine, which is an amino acid useful as a medicament (e.g., an amino acid preparation), an additive for animal feed, etc.
2. Description of the Prior Art
Heretofore, various processes for producing L-threonine by fermentation have been known; for example, a process using a microorganism belonging to the genus Escherichia and having sensitivity to borrelidin (Japanese Published Examined Patent Application No. 6752/76), a process using a microorganism belonging to the genus Escherichia which requires diaminopimelic acid and methionine and of which threonine biosynthesis system is resistant to the feedback inhibition of threonine (Japanese Published Examined Patent Application No. 10037/81), a process using a microorganism belonging to the genus Serratia which is deficient in threonine-dehydrogenase and resistant to threonine metabolism-antagonist (Japanese Published Examined Patent Application No. 48195/77), a process using a microorganism belonging to the genus Corynebacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine, and a requirement for methionine (Japanese Published Unexamined Patent Application No. 19087/72), a process using a microorganism belonging to the genus Brevibacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine, and a requirement for leucine (Japanese Published Unexamined Patent Application No. 31093/75), a process using a microorganism belonging to the genus Brevibacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine, and requirements for L-isoleucine and L-lysine (Japanese Published Unexamined Patent Application No. 224684/83), etc.
However, the known processes are still insufficient in efficiency of the production of L-threonine.
It is therefore an object of the present invention to provide a process for producing L-threonine in higher yield and at low cost.